Exposure to intense ultraviolet light to improve characteristics of cellulosic fabrics in divinyl sulfone and glyoxal cross-linking processes



United. StatesPatent Ofiice.

3,357,784 Patented Dec. 12, 1967 Andrew A. Kasper, Watertown, Mass, assignor to The Kendall Company, Boston, Mass, a corporation of Massachusetts No Drawing. Filed Sept. 30, 1964, Ser. No. 400,548 Claims. (Cl. 8-116..4)

It has long been common in the textile industry to treat cellulosic fabrics such as those composed of cotton or rayon with certain reagents which increase the resilience of the fabrics, making them less prone to creasing or wrinkling, and simultaneously minimizing the progessive shrinkage which occurs in laundering, particularly in the case. of rayon fabrics. Such reagents as urea-formaldehyde, melamine-formaldehyde and the triazone resins are widely used: epichlorhydrin, formaldehyde, and divinyl sulfone are reagents of the reactant type, sometimes distinguished from reagents of the resinous type. The reagents of the resinous type, applied to cellulosic fabrics, tend to develop unpleasant and persistent odors in the fabric: their degree of fixation on the fabric is not secure, the resin content gradually decreasing by wash down as the fabric is repeatedly laundered: many of them are sensitive to a chlorine bleach: and they unduly stiffen and embrittle the fabric.

Reagents of the reactant type are primarily not resin precursors, but are smaller mobile molecules with active groups which tend to react with the hydroxyl groups of the cellulose molecule, thereby crosslinking various elements of the cellulose chain to stabilize the fibers and hence the fabrics. The. application of some reactants is expensive and hazardous. Formaldehyde is relativelyinexpensive, but does not crosslink or react with cellulose in a permanent fashion until a critically low pH of about 3.0 is reached. This results in appreciable tensile loss in fabrics thus treated, which together with the irritating and toxic nature of formaldehyde vapors, mitigates against more widespread use of this reagent.

Many attempts have been made to utilize glyoxal, (CHO) to react with cellulose. One of the earliest mentions is in the 1,857,263 US. patent of May 10, 1932, to Sponsel, who dried dilute solutions of glyoxal on rayon fabrics and found an increase in strength. He makes no mention of having obtained any creaseproofing or nonshrinking effect. Groves, in British Patent 439,294, of Dec. 4, 1935, indicates a good resistance to creasing developed in a cotton fabric by soaking the fabric in a solution of glyoxal and calendering it at 110 C. (230 R). US. Patent 2,412,832, of. Dec. 17, 1946, to Pfefier et al., also discloses the use of glyoxal to stabilize cellulosic fabrics.

However, it has hitherto been difiicult if not impossible to utilize glyoxal in a convenient commercial. process for imparting wrinkle-resistance and shrinkage-resistance. 1

to cellulosic fabrics without excessive embrittlement and tensile strength loss accompanying the reaction. The disclosed art has suggested various pH ranges of operation, various drying-curing temperatures, various catalysts such as metallic salts, and various adjuncts and additives to moderate the reaction. None of these suggestions has pro vided a solution to the problem of tensile strength loss.

As is pointed out by Hurwitz and Condom (Textile Re-: i search Journal 28, 257466, 1958), all heat-promoted dial-I dehyde reactions with cellulose approach the performance of formaldehyde: that is, crease-recovery as measured by Monsanto angle of 250 or higher, but with an unsatisfactory tensile strength loss of 60% or more. For satisfactory commercial fabrics this tensile strength loss should be cut in half, since it is normal expectation in the trade that a product such as a resin-treated shirting broadcloth is commercially acceptable with a tensile strength loss of 30% to Losses of and over, however, lead to premature Wearing-out of garments, and are not acceptable.

It is an object of this invention to provide a process whereby glyoxal may be reacted with cellulose to give a fabric which meets acceptable commercial standards of wrinkle-recovery and shrinkage-resistance while displaying only a loss in strength associated with most Washwear resin finishes, said loss being recognized and considered acceptable by the trade.

All prior attempts of which I am aware .to promote a t and glyoxal can be obtained with. a fabric strength loss that is acceptable. The reaction may be carried out using organic solutions of glyoxal, but for obvious. commercial reasons, aqueous solutions are preferred. Catalysts, wett ting agents, and other reaction accelerators or modifiers may be employed in the conventional manner.

In addition to glyoxal, I have found that the reaction between cellulose and divinyl sulfone is promoted by ultraviolet light, in a manner. set forth below.

GENERAL STATEMENT OF THE GLYOXAL REACTION and is baked to dryness over the course of 1% to 2 minutes in a circulating hot air oven adjusted to about 150 C.

The dry sample is. then irradiated with a stream of photons of Wave length 2,800 to 4,000 Angstrom units, with the 2,800 to 3,200 Angstrom units range being par- 1 ticularly effective due to. the heightened sensitivity of glyoxal and parabromoacetophenone in this region. The stream of photons is conveniently derivcdfrom a bank of sun lamps of the type which provide an average photon density of 10 to 10 photons persecond per square centimeter. Irradiation is continued for from 4 to 9 min- 3 utes, after which the sample is washed and tested for crease recovery by the well-known Monsanto angle recovery test, explained below. In general dry Monsanto angles (combined warp and filling) of 280-290 are realized, wet Monsanto angles of 250 or more, and a tensile strength loss of 35% or less.

TEST METHODS Fabrics treated in accordance with the process of this invention were tested for crease recovery by the so-called Monsanto Tester, accepted by and described in Federal Specification CCCT-l9lB (M5212), and in A.S.T.M. D1295-53T. Samples of fabric 1.5 by 4.0 centimeters are cut from the fabric in both warp and filling directions, conditioned at 70 F. and 65% RH. for at least 4 hours for the dry Monsanto angle, or immersed in water containing a few drops of detergent solution for at least 30 minutes for the wet angle test.

The sample is creased at 180 and compressed under controlled conditions of time and load. After five minutes recovery, the recovery angle is measured. The reported Monsanto angle is the sum of Warp plus filling tests, 360 representing complete restoration in warp and filling.

Tensile strength determinations were made on the Instron machine.

VARIABLES IN THE PROCESS As base fabrics suitable for treatment by the process of this invention there may be mentioned conventional cotton fabrics such as broadcloths, poplins, sheetings, and print cloths: rayon fabrics such as rayon challis or sateen: fabrics containing blends of cotton and rayon, either fiberto-fiber blends or yarn blends: and blends of cellulosic with non-celluolsic fibers provided that in the blend there is a sufficiently substantial percentage of reactive cellulosic fibers to be effective, generally 35% or more. The fabrics should be sufficiently purified from the grey loom state to allow the fibers to absorb the glyoxal solution. Mercerization before conducting the process of this operation has the beneficial elfeet of increasing the Monsanto angles by about and reducing the tensile loss by about 10% presumably by fiber swelling and the opening-up of new reaction sites inaccessible in native cellulose.

Glyoxal is available as a 40% aqueous solution commercially, in which solution it is generally regarded to be hydrated to a cyclic structure known as tetrahydroxy naphthodioxane. The heating and dehydrating stage of the present process regenerates glyoxal.

Depending on the degree of crease recovery desired, balanced against the tensile strength loss that can be tolerated, glyoxal add-ons of from 1% to 10% based on fabric weight are of interest in the practice of this invention, with a preferred range of 3% to 8%. In general, as the glyoxal add-on is increased from 3% to 8%, the wet Monsanto angle increases and the tensile strength loss decreases. In the vicinity of around 8% or 10%, a plateau is reached in crease resistance, and increasing the glyoxal content of the fabric above this point does not bring about a corresponding improvement in the fabric.

The zinc chloride in the impregnating bath seems to serve one particular purpose, which is to increase the permanence of the wet Monsanto angle. Irradiated products where zinc chloride has been omitted have high dry Monsanto angles, and high Wet Monsanto angles after brief immersion of up to 30 minutes in water. However, the bond between the glyoxal and cellulose formed in the absence of zinc chloride shows an apparent hydrolysis of up to 80% over 60 to 80 hours, as indicated by a steadily decreasing wet Monsanto angle, even though sufficiently high dry Monsanto angles are attained. Since there are fabrics such as draperies and the like which are meant to be dry-cleaned and not laundered, there are obviously cases wherein only the dry Monsanto angle is of concern. Therefore I regard the use of zinc chloride as optional,

depending on the nature and end-use of the fabric, and do not wish to be restricted to its use. As an example of the effect of zinc chloride, the general procedure above was duplicated with 5% glyoxal, .06% parabromoacetophenone, 2% minutes drying at C., 7 minutes irradiation, and with a similar solution containing 0.75% zinc chloride and 1.25% formic acid. The dry Monsanto angles were about the same, 300. The immediate wet Monsanto anglethat is, the angle measured after 30 minutes immersion, was 250 in each case. However, on longer soaking of 64 hours, the wet Monsanto angle was 240 in the case of the sample run with zinc chloride, whereas it decayed to 200 in the case of the sample run without zinc chloride. By periodic. measurements, the rate of decay of the wet Monsanto angle was determined to be about 5% of the initial value per hour of immersion for samples not treated with zinc chloride.

Other acidic salts which may replace the zinc chloride include the other zinc halides (except the fluoride), zinc sulfate, zinc nitrate, magnesium chloride, and magnesium nitrate. In general, the effective range of concentration of the zinc chloride is from 0.25% to 2 or 3%. At the higher range, the tensile strength loss is liable to be excessive, so a range of 0.5% to 0.8% zinc chloride is preferred as resulting in adequate stabilization of the wet Monsanto angle combined with minimum tensile loss.

The exact mechanism by which zinc chloride stabilizes the cellulose-glyoxal bond is not known to me. It may be of significance that approximately equal stability may be attained by including the zinc chloride in the initial impregnating bath, curing, and irradiating, or by impregnating without zinc chloride, curing, irradiating, saturating with dilute zinc chloride solution, and recuring. The effect therefore is probably an independent effect on the nature of the bond, rather than a modification of the initial cellulose-glyoxal reaction.

The use of formic acid in the impregnating bath is advantageous principally when zinc chloride is used. Zinc chloride alone in the reaction hasbeen found to hydrolize to a certain extent to basic zinc chloride, which precipitates onto the fabric and which has been reported to be more acidic than zinc chloride itself. In the drying operation this acidity causes additional tensile strength loss. The presence of formic acid or similar material apparently prevents the formation of basic zinc salts, and helps preserve tensile strength.

The parabromoacetophenone, present in trace quantities, is desirable as a sensitizer to promote the photoninduced reaction between cellulose and glyoxal. Photosensitizers in general have the property of absorbing spectral energy at some given wave length, being thereby lifted from their normal or ground states to excited states. In the excited state, a photosensitizer is postulated to enter into an energy change with a second substance, in this instance glyoxal, thereby raising the reactant to an activated or excited stage and facilitating the reaction between the reactant and the cellulose molecule.

In addition to parabromoacetophenone, sensitizers such as benzophenone, acetophenone, and chloranil may be employed. They should be regarded as facilitating the reaction, rather than as being essential to it. Where dry Monsanto angles of around 280, wet angles of around 240", and tensile strength losses of 40% or so are allowable, the sensitizer may be omitted. Its use does, however, promote the realization of wrinkle-resistant fabrics of high commercial acceptability.

I have found that the drying-baking step of the impregnated material, prior to irradiation, is an essential and critical step. The exact chemical nature of simple aldehydes in aqueous solution has not been explicitly determined. As set forth above, some authorities believe that in the presence of water, two molecules of glyoxal hydrate with two molecules of water to form tetrahydroxy naphthodioxane. Others have postulated a simpler reaction wherein two molecules of water hydrate a single molecule of glyoxal to form tetrahydroxy ethylene. Regardless of the particular hydrated aldehyde species present on the saturated fabric, it must be dehydrated to the simpler dialdehyde form before reaction with the cellulose. A

6 1 5% glyoxal (aqueous) containing 0.06% parabromoacetophenone and 1% zinc chloride, air dried, and cured at 170 C. in a circulating air oven for 70 seconds.='I'he Wet Monsanto angles after 30 minutes immersion in water mere air-drying to normal moisture regain is not suflicient 5 plus detergent were excellent, the sum of Warp and filling to promote a desirable cellulose-glyoxal reaction, which angles being over 300 The tensile strength loss, how is why I have referred to this step as a dry-bake process, ever, was unbearably excessive, being 69%, and the fabric rather. than drying. It has been my experience that the was so brittle as to be friable and commercially worthmoisture content of the dried fabric m t be red to less. A similar set of fabric samples was impregnated with at1ea5t2-5% and Preferably ioibelow optlmufn 10 an aqueous 5% solution of glyoxal plus 0.06% parabroi results. This moisture content is below the normal regain moacetophenone without zinc chlorids, to 1Q[) 100% f a faPnc that has been 1mP1Y air afterfmpregn? pickup, and air-dried. The samples were then irradiated m with a glyoxfll Sohmon' m be that a by radiation from a bankof ultraviolet sun lamps for with normalregam, the most available potential react1ve 7 minutes after which they Wem dipped into 1% Zinc. mes are assoclated loosely'bound adsorbed wafer chloride solution, squeezed to 100% pickup, air-dried,.and molecules and that thls type of hydration competes with heated in a circulating air oven for 60 seconds Thewet the desired glyoxal-cellulose reaction. Whatever the rea- M t 19 ft r minutes immersion'in water son, it appears that removing a substantial part of the lonsan o ang 2 b1 1 normal regain moisture facilitates a more extensive and P us deteigentt was an accept?" e commercla f a more durable wrinkle-resistant effect when cellulose is 20 and the Slength was only also commerclauy re with glyoxal which has been applied fr an acceptable level, said acceptable commercially acceptable aqueous l i Thi i borne out b h foll i levels of wrinkle-resistance and maintenance oftensile Table 1, showing the effect of various pro-irradiation con- Strength being l' chaljacterlstlc Q the Products ditions on the crease-resistance of a standard fabric. made according to this lIlVGIlilOIl.

TABLE I" Percent Tensile Monsanto Angle Wet,

Drying Condition Irradiation Add-0n Loss, Dry, deg. deg.

. percent None 7:2 10 241 220 Room temperatu.re 6.9 24 262 240 Warm Air 7. 0 33 277 259 Circulating, 100 C. air I 7:5 33 285 27 When ,glyoxal has been applied froinian acetone solu- THE DrvmYLsULFoNa REACTION there is apparently a semi'bhydmfing acnon. the Divinyl sulfone is known to, react withcellulose,-as set -1 st Presumably me mutual SOMbhtY of forth in US. Patent 3106439 of Oct. 8 1963. However, acetone .and water, and a cellulosic fabric saturated with as pointedout in that i h reactiofimust be carried a glyoxabacetone solution may be irradiated wet without 40 out in an alkaline medium: at a 35 or higher the need f Preiwanng Under such conditions, the reaction is accompanied by For the rradlatlon Step5 .ltravlolet g m the regltm side reactions which cause more or less extensive dis- 2 from 2800 -"P umts Angstrm,umts coloration of the fabric, which must be subjected to a $223 'ifig m ggigi g i g g s gg $3 1? if thorough scouring after reaction to restore itsicolor to an t 1 n o r excitationyreacfiom e g e e g e acceptable commercial level.

I have found that divinyl sulfone can be crosslinked '(CHO) +h1/=(CH0) with cellllostillndeg acid conditions, anetlI without the fpra p mation o co ored y products, if a sin 1 amount of g y- 2 332 f ;2 22 9 g i i f gg oxal is present as an activator or sensitizer, and provided 195;) zg i 7 i 5O thatthe impregnated sample is irradiated with ultraviolet h v r g yoiia as e m pa light during the reaction. The preferred generalprocedure 1 acts Wlt fi i m part 15 i to Photolytlc is to impregnate the fabric with a mixture of diviriyl decomposition according to the following reactions: sulfone, glyoxal, and formic acid; then in the Wet condi (CHO) *=H +CO tion and on a thermally controlled surface. the fabric is (CHO) =HCHO+C0 V irradiated for several minutes, Washed, and dried. the latter reaction being more probable. In the latter case, er gf g i g g 3 9 3;: the formaldehyde formed by photolysis can itself react u f erre 5 f O with the cellulose molecule to give cross'linking. The 3 can ramps gf t g m g d system therefore is very 'eflicient in light-energy utilizab 5 3 8 25 lfig k e m e fz tron, andthe photo-induced reaction glyoxal and cellufgund 5 52 1 relic if is z g z g lose eifects a combination of maximumv glyoxal add-on nder n g i P F erre]? with minimum tensile strength loss which cannot be re- 3 t 3E 6 mac con 2 g i a alized by any other process with which I am familiar. g m gommema accep a e Onsan 0 7 The activating influence of ultravioletradiatio e1 er does t e use of divmyl sulfone aloneA mixture n In t is f 3 5 65 o to parts of dlVlHYl. sulfone to 1 part. of. glyoxal, reaction is quite dllterent from the influence of the infrahowever is eflenfive in acid medium in imparting an r a v a i g red irradiation previously used 1n glyoxal-c f" acceptable crease-proofing property to cellulosic fabrics, actions in which the driving force: is purely thermal, as in as Set forth below in Example conventional curing or baking reactions. The following example will illustrate the diiference between irradiation Emmplez plus curing and purely thermal curing.

Example 1 A sample of the -square print cloth of Example 1 was 1 impregnated with anaqueous solution of 9.8% divinyl sulfone, 2% glyoxal, and 5% formic acid. The wet pick up was adjusted to While still wet, the sample was placed on a metal surfaceheated to 210 F. and irradiated for 7 minutes under a bank of ultarviolet sum lamps. The dry product was then thoroughly washed in a dilute solution of sodium carbonate and detergent, rinsed to neutrality, and dried. The cloth had increased in weight by 5.4%; the tensile strength loss was 37%; dry Monsanto angle was 285; and the wet Monsanto angle after soaking the fabric 86 hours in detergent solution was 240. The fabric had no odor, was not discolored, and the finish was resistant to hydrolysis as evidenced by retention of high Monsanto angle after immersion for 84 hours in aqueous solutions varying in pH from 3.5 to 11.0.

In addition to formic acid, other acids may be used provided that a pH solution range. of 1.5 to 3.5 can be thereby realized. Suitable acids include oxalic, malic, maleic, tartaric, fumaric, citric, and chloracetic.

Although the reaction of Example 2 was carried out without a sensitizer, parabromoacetophenone and sensitizers of analagous action may be utilized, in concentrations of 0.01% to 0.06%, to accelerate the reaction.

I am aware that it has been proposed to promote grafting reactions between cellulose and resin precursors by the use of high energy radiation. High energy electron beams, however, are in the class of ionizing radiation, and in general their use leads to ionization of at least one of the reactans, and to secondary chemical changes. The ultraviolet irradiation of this invention is substantially non-ionizing, the energy density is lower, and the net effect is the promotion of a cross-linking between cellulose and reactant, rather than the promotion of a surface grafting of a polymer onto cellulose.

Having thus described my invention, I claim:

1. A process of producing a crease-resistant finish on a cellulosic fabric which comprises impregnating said fabric with a reactant selected from the group consisting of glyoxal and divinyl sulfone containing a sensitizing amount of glyoxal and subjecting the impregnated fabric to ultraviolet irradiation of an intensity of at least photons per square centimeter per second for a period of from 4 to 9 minutes.

2. A process for producing a crease-resistant finish on a celulosic fabric which comprises impragnating said fabric with an aqueous solution of glyoxal, drying said fabric, and subjecting said fabric to ultraviolet irradiation of an intensity of at least 10 photons per square centimeter per second for a period of from 4 to 9 minutes.

3. A process according to claim 2 wherein the impregnated sample is dried to a moisture content below its normal regain level prior to irradiation and is maintained at said lower moisture level during irradiation.

4. A process for producing a crease-resistant finish on a celulosic fabric which comprises impregnating said fabric with an aqueous solution comprising glyoxal,

in an amount and at a concentration suflicient to equal between 1% and 10% of glyoxal, based on the weight of said fabric,

said aqueous solution also comprising between 0.25%

and 3.0% of an acidic salt catalyst,

and between 1% and 2% of an organic acid;

drying said impregnated fabric to a moisture content below 2.5%;

and maintaining said fabric at or below said 2.5%

moisture content while subjecting said fabric for a period of from 4 to 9 minutes to ultraviolet irradiation of an intensity of at least 10 photons per square centimeter per second.

5. A process according to claim 4 in which the acid salt catalyst is zinc chloride and the organic acid isformic acid.

6. A process according to claim 4 in which the aqueous solution comprises, in addition to glyoxal, acid salt cata lyst, and organic acid, a trace amount of a photosensitizing agent.

7. A process according to claim 6 in which the photosensitizing agent is chosen from the class consisting of benzophenone, acetophenone, chloranil, and parabromoacetophenone.

8. A process for producing a crease-resistant finish on a cellulosic fabric which comprises impregnating said fabric with an aqueous solution comprising divinyl sulfone, glyoxal, and an organic acid sutficient to reduce the pH to at least 3.5,

and irradiating said impregnated fabric for a period of between 4 and 9 minutes at a temperature of at least 200 F.

with ultraviolet radiation of an intensity of at least 10 photons per square centimeter per second.

9. A process according to claim 8 wherein the impreg nating solution contains between 3 and 5 parts of divinyl sulfone per part of glyoxal and the acid is formic acid.

10. A process for producing a crease-resistant finish on a cellulosic fabric which comprises impregnating said fabric with an aqueous solution of glyoxal,

drying said impregnated fabric,

' reducing the moisture content of said fabric below 2.5% while simultaneously subjecting said fabric to intense ultraviolet irradiation of an intensity of at least 10 photons per square centimeter per second for a period of from 4 to 9 minutes,

immersing said fabric in an aqueous solution of an acidic salt catalyst,

and drying and curing said fabric.

References Cited UNITED STATES PATENTS 1,857,263 5/1932 Sponsel et al. 8116.4 2,436,076 2/1948 Pfelfer et al. 81l6.4 2,484,545 10/ 1949 Beer 8116.4 2,521,328 9/1950 Beer 8-l16.4 2,530,175 11/1950 Pfeflieret al. 8l16.4

OTHER REFERENCES Egerton: J.S.D.C., vol. 63, pp. 161-171 (1947). Egerton: J. Textile Inst., vol. 39, pp. T293-T304 (1948).

Egerton: J.S.D.C., vol. 65, pp. 764-780 (1949).

I. TRAVIS BROWN, Acting Primary Examiner.

NORMAN G. TORCHIN, Examiner.

J. C. CANNON, Assistant Examiner. 

1. A PROCESS OF PRODUCING A CREASE-RESISTANT FINISH ON A CELLULOSIC FABRIC WHICH COMPRISES IMPREGNATING SAID FABRIC WITH A REACTANT SELECTED FROM THE GROUP CONSISTING OF GLYOXAL AND DIVINYL SULFONE CONTAINING A SENSITIZING AMOUNT OF GLYOXAL AND SUBJECTING THE IMPREGNATED FABRIC TO ULTRAVIOLET IRRADIATION OF AN INTENSITY OF AT LEAST 10**14 PHOTONS PER SQUARE CENTIMETER PER SECOND FOR A PERIOD OF FROM 4 TO 9 MINUTES. 